The present invention relates to the imaging of lithographic plates and, more particularly, to conditioning a lithographic printing plate substrate for imaging in a conventional, commercially available electrostatic printer or ink-jet printer.
Imaging of lithographic printing plates by electrostatic or ink-jet printing has been the subject of extensive research and development and has been commercialized to some extent. In the case of electrostatic imaging, a toner is applied to an electrostatic image formed on a lithographic plate substrate and is then fused. Similarly, the desired image can be formed and then fixed on a suitably prepared substrate by ink-jetting a fluid. The toner or ink-jet image on the substrate is either receptive or repellant to a printing ink, depending on the nature of the surface of the plate substrate to which the image is applied and fixed. The substrate may or may not include a coating suitable for receiving toner or ink jet fluid. An important advantage of electrostatic or ink-jet imaging is the current availability of machines (electrostatic copier/printers and ink-jet copier/printers) that can be readily adapted for use in imaging lithographic plate substrates.
Lithographic printing machines and processes require plates that are highly dimensionally stable and durable, which inherently makes them relatively thick and stiff. Currently available electrostatic and ink-jet printing engines, on the other hand, are designed to handle relatively thin, flexible materials, such as paper, thin plastic films, or metal foils. Substrates suitable for lithographic printing plates may be too stiff or thick to be reliably inducted into and transported in many available printing engines.
An object of the present invention is to provide an article suitable for imaging in currently available electrostatic and ink-jet printer engines to make a lithographic printing plate. More particularly, it is an object to condition a lithographic plate substrate so that it will be reliably inducted and transported by the sheet-transports of such printer engines. It is also an object to provide a plate substrate that is conditioned in a very simple, economical and effective way to feed through printer engines for imaging.
As used hereinafter, the term xe2x80x9cprinter enginexe2x80x9d means an apparatus that is capable of transporting sheet material and forming an image or the sheet material by placing a substance on the sheet material by electrostatic or ink-jet deposition.
The objects referred to above are attained, in accordance with the present invention, by an article for use in preparing a lithographic printing plate by imaging in a printer engine. The article includes a lithographic plate substrate and a leader attached to and projecting from a leading edge of the plate substrate, the leader being sufficiently flexible to be drawn into the printer engine and being adapted to pull the plate substrate through the printer engine.
It has been found that even though many presently available printer engines may not accept and transport the relatively thick and rigid plate substrates required by lithographic printing machines for durability, such plate substrates will transport properly and reliably with a leader according to the invention. The leader may be of any thin material that will itself (without the plate substrate that is to be imaged) be picked up and transported by the printer engine. The leader need not itself be especially durable, because it need only xe2x80x9cleadxe2x80x9d the plate substrate through the printer engine and will be removed after the plate substrate is imaged. The provision and use of the leader involves a comparatively negligible cost and avoids the need for the costly development and production of special printer engines for imaging lithographic plates.
The plate substrate may be of a high-density polymeric material, a coated paper, or a metal, such as aluminum, tin or copper. The leader may be paper, a film of a polymeric material, or a thin metal film or plate substrate. In the case of electrostatic imaging, the leader must be of a material that will not melt during fusing of the toner. The leader may be attached to the plate substrate by an adhesive, which may be a self-sticking adhesive that is detachable from the plate substrate without marring the plate substrate or an adhesive that aggressively and more or less permanently attaches the leader to the plate substrate. In the latter case, the leader is severed from the plate substrate after the plate substrate has been imaged.
The leader may be a strip of material having a portion overlapping the plate substrate and may be attached to the plate substrate by in adhesive on the overlapping portion. It is also possible for the leader to be a strip of material forming a butt joint with the leading edge of the plate substrate and attached to the plate substrate by a band of an adhesive tape on one side or bands of adhesive tape on both sides.
In a particularly desirable embodiment, the leader is a strip of an adhesive tape having a portion overlapping and adhered to the plate substrate and a portion extending from the leading edge of the plate and doubled back on itself such that a free edge of the doubled back portion forms a butt joint with the leading edge of the plate substrate. The adhesive tape may be a paper adhesive tape, which provides a desirable surface for induction and transport by the printer engine and avoids any possible problem of melting or softening in the fuser of an electrostatic printer engine.
The leader may project from the leading edge of the plate substrate by a distance of from 0.125 inch to 10 inches. The amount of the projection will depend on the sheet-transport structure of a particular printer engine. It has been found generally that a projection of about 0.5 to 1.0 inch is sufficient. It is usually desirable that the leader be substantially coextensive widthwise with the leading edge of the plate substrate.
The foregoing description has outlined rather broadly some features and advantages of the present invention. The detailed description of embodiments of the invention that follows will enable the present invention to be better understood and the present contribution to the art to be more fully appreciated. Those skilled in the art will recognize that the embodiments may be readily utilized as a basis for modifying or designing other structures and methods for carrying out the purposes of the present invention. All such structures and methods are intended to be included within the spirit and scope of the invention as set forth in the appended claims.